A widespread problem is the presence of water in petroleum fuels for internal combustion engines. Although undesirable water is often present in engine fuel tanks, especially as a result of condensation. The presence of water is recognized as particularly harmful in the fuel injectors of diesel engines, which are normally protected by separators in the fuel feed line for removal of water before it reaches the engine. Such water separators are conveniently provided with foraminous filter walls, which pass the fuel but hold back the water for periodic discharge (as disclosed, for example, in U.S. Pat. No. 4,637,351). Rotatable devices for centrifugal separation of water from fuel are disclosed, for example, in U.S. Pat. Nos. 1,731,313; 2,984,410; 3,014,643; 4,106,689; 4,288,030; 4,346,009; and 4,344,561. However, foraminous filters have to be replaced from time to time, and rotating devices are relatively complex and expensive.